An image recording apparatus which uses ink to record images on a sheet (recording medium) has been known as a related art. Such image recording apparatus includes an ink jet recording head, and selectively discharges ink droplets onto a recording sheet from nozzles of the recording head. The ink droplets are dropped on the recording sheet, and a desired image is recorded on the recording sheet. The image recording apparatus is provided with an ink container which stores ink to be supplied to the recording head. The ink container is generally a cartridge type, and can be inserted into or removed from a cartridge mounting portion provided in the image recording apparatus. This type of ink container is referred to as ink cartridge. When there is no ink in the ink cartridge, the ink cartridge is removed from the cartridge mounting portion of the image recording apparatus, and a new ink cartridge having ink stored therein is inserted into the cartridge mounting portion. The ink cartridge inserted into or removed from the cartridge mounting portion includes a hole which allows the inner space of the ink cartridge to communicate with the outside and a cover which seals the hole, and the cover is opened by, for example, an ink needle. In a configuration in which the cover sealing the hole is opened or closed by, for example, a valve, when the ink cartridge is removed from the cartridge mounting portion, the hole is closed, and ink is stored in the ink cartridge without leakage. On the other hand, when the ink cartridge is inserted into the cartridge mounting portion, the hole is opened, and ink can flow from the ink cartridge to the outside.
JP-A-3-234653 describes an ink supply system of a facsimile device in which a cartridge joint 79 is provided on a base 73 and a metal ball 99 is pressed against a joint opening 95a of an ink cartridge 86 by a spring 98. When the ink cartridge 86 is removed from the base 73, the joint opening 95a is sealed by the metal ball 99. When the ink cartridge 86 is inserted into the base 73, the cartridge joint 79 presses the metal ball 99 against the urging force of the spring 98, and the joint opening 95a is opened.
JP-A-2007-500619 describes a liquid interface having a ball seal structure. The liquid interface seals the contents of an ink cartridge. When a hollow needle is inserted to the liquid interface, the liquid interface drains the contents of the ink cartridge through the hollow needle.
As described above, the cartridge mounting portion to which the ink cartridge is inserted is provided with a cylinder which is inserted into the hole of the ink cartridge, such as a cartridge joint or a hollow needle. The leading end of the cylinder presses, for example, a ball of the ball seal structure which opens or closes the hole of the ink cartridge, thereby opening the hole. For example, as shown in FIG. 20 of JP-A-2007-500619, contact surfaces which contact the ball and cutouts through which ink flows are provided at specific intervals in the tip surface of the hollow needle in the circumferential direction of the hollow needle.
The ball seal structure is provided with, for example, members, such as a spring which urges the ball and a guide which guides the movement of the ball. The members of the ball seal structure are exposed to an air layer of the ink cartridge due to the packed state or the vibration of the ink cartridge while being transported, and air bubbles may be attached to such members. With the ink cartridge being inserted into the cartridge mounting portion, the members of the ball seal structure are kept being soaked in ink. However, the air bubbles attached to the members of the ball seal structure do not float in the ink, but are maintained in the attached state. In this case, when the air bubbles are drained from the ink cartridge together with ink, ink flow defects or ink discharge defects may occur in an ink passage or a recording head of an ink-jet printer.